The invention relates to a wind energy conversion apparatus comprising a supporting structure including a number of spokes, which is rotatably journalled on a horizontal main shaft, wherein wind capturing means having an at least substantially circular plane of inflow are mounted on the ends of said spokes.
Wind energy conversion apparatuses of the kind referred to above have been known for quite some time already in the form of the well-known windmills and wind turbines. The wind capturing means that are used thereby are usually in the form of wings or rotor blades, which are rotatable about a horizontal main shaft. The horizontal main shaft thereby extends in the direction of the oncoming wind, all this in such a manner that the plane of inflow of said wind capturing means extends substantially perpendicularly to the main shaft and also substantially perpendicularly to the direction of the oncoming wind.
For a long time already people have attempted to convert an increasing amount of wind energy into other forms of energy. It is known that this can be achieved by enlarging the area that is covered by the wind capturing means. This can be accomplished by using wings or turbine blades having a greater length. The large mechanical forces that act on such long wings or turbine blades place limitations on said length, however.
Another way of enlarging the area covered by the wind capturing means is known from WO 96/00349, FIGS. 10 and 11. Said document discloses a wind turbine comprising a supporting structure (main rotor) including spokes, which is rotatable about a horizontal main shaft and wherein auxiliary rotors are disposed on the ends of said spokes. Said auxiliary rotors, which function as wind capturing means, are thereby so positioned that their plane of inflow extends perpendicularly to the main shaft. A large area is covered with this construction, whilst the length of the rotor blades can be relatively small, so that the mechanical forces that are exerted on said blades can be kept within bounds, especially when, as is also shown, the main rotor and the auxiliary rotors are rotated in opposite directions. The wind capturing means, in this case the auxiliary rotors, of said prior art turbine cover a very large area, as a result of which a large amount of energy is extracted from the oncoming air.
The object of the invention is to improve the aforesaid prior art apparatus and to provide a wind energy conversion apparatus which, given the same dimensions and the same wind conditions, is capable of converting a larger amount of wind energy into other forms of energy.
In order to accomplish that objective the wind energy conversion apparatus according to the invention is characterized in that each of said wind capturing means has a plane of inflow which includes an acute angle with the central axis of the main shaft and which intersects said main shaft upstream.
Surprisingly, said inclined position of the wind capturing means, which, as will be explained in more detail yet, may be made up of rotors including rotor blades, which are disposed on the spokes of the supporting structure, or of conical bodies having a large apex angle, such that their planes of inflow include an acute angle with the central axis of the main shaft of the supporting structure, leads to an increased mass flow passing the wind energy conversion apparatus, which in turn leads to an increased energy output. All this can be traced back to the fact that the inclined position of the wind capturing means creates an underpressure near the main shaft, which leads to a certain contraction of the oncoming wind. As will be explained in more detail yet in the description of the figures, all this leads to a significant increase of the energy output that can be obtained from the oncoming air.
Another embodiment of the wind energy conversion apparatus according to the invention is characterized in that each of the wind capturing means consists of a rotor having at least two rotor blades, wherein each rotor is mounted on a rotor shaft, which is rotatably journalled on the end of an associated spoke in such a manner that the plane in which the rotor blades lie includes an acute angle with the central axis of the main shaft and intersects said main shaft upstream, wherein the rotor shaft of each rotor is coupled with means, such as a generator, for converting rotation energy into electric energy. Also in this embodiment of the apparatus according to the invention the aforesaid effect of contraction of the oncoming air flow will occur, resulting in an increased mass flow through the rotors and thus an increased energy output.
According to another embodiment of the apparatus according to the invention the main shaft of the supporting structure includes means for rotating the same. Said means may consist of an electric motor, which is capable of rotating the supporting structure. In this manner it is not the wind velocity but the electric motor that determines the speed of the main rotor, thus enabling easy protection and control the apparatus.
In another embodiment of the apparatus according to the invention the wind capturing means are conical bodies having a large apex angle, whose base is directed towards the oncoming wind, which conical bodies are connected to the ends of their associated spokes in such a manner that the base of each conical body includes an acute angle with the central axis of the main shaft of the supporting structure, intersecting said central axis upstream of the main shaft. Owing to the inclined position of the bases of the conical bodies relative to the main shaft, an area of lower pressure is created round the main shaft again, resulting in an increased mass flow of the air that passes the conical bodies and consequently in an increased energy output.
Another embodiment of the apparatus according to the invention is characterized in that a number of spokes of the supporting structure carry a rotor and in that a number of spokes have a conical body mounted thereon.
According to the invention the acute angle that the aforesaid wind capturing means include with the central axis of the main shaft is adjustable between 80xc2x0 and 10xc2x0, preferably between 60xc2x0 and 30xc2x0.